SAN and NAS: Together At Last

For many years, the major storage vendors had either a SAN solution or a NAS solution. Few, if any, had both. The SAN (storage area network) vendors would bash NAS (network attached storage) solutions and the NAS vendors would bash the SAN solutions.

Now, most of the major storage vendors have both solutions available and the rhetoric has lessened, instead of trying to sell the only solution, vendors are more likely to present the best solution for the customer’s environment.

Before SAN and NAS existed there was just internal storage (disks enclosed within a server) or small SCSI-attached DAS (direct attached storage) devices and companies bought storage with their server purchases. NAS was a Novell, UNIX or Windows server sharing data over an IP network. A very crude SAN could be created by attaching more than one host (usually no more than four) to a DAS device.

The NAS market was originally spearheaded by Auspex, which closed shop in 2003, while NetApp is credited with NAS’s widespread adoption. Today, all of the major storage vendors offer NAS solutions. SANs, which utilize FC (Fibre Channel) architectures, didn’t start appearing until the late 1990s.

The FC standard was approved in 1994 but SANs were slow to appear. It was the late ’90s to 2000 before the SAN market exploded. Today, FC is widely deployed and SANs are commonplace.

What is a SAN?

A SAN is a FC network dedicated to storage (primarily disk and tape). Historically, companies would have open systems servers with internal hard drives or DAS. A server with its own, dedicated storage is called an “island” of storage. Each server managed its own storage and was unable to share unused capacity.

This kind of deployment led to a lot of storage overhead. With a SAN, servers and storage are attached to FC switches. The server has a special FC host bus adapter (HBA) to communicate with the SAN, which handles the I/O load and leaves the CPU to process the application requests. Because of this, SAN storage performs as fast as, or faster, than internal storage and allows multiple servers to share the same physical storage pool to allow more efficient utilization of the resources.

Currently, SANs support 1Gb, 2Gb and 4Gb connectivity between devices (servers and storage). There are some switches available that support 10Gb inter-switch links. SANs are useful for environments that need large capacities, block access to data, have multiple servers and/or require high performance.

Okay, So what is a NAS?

While a SAN is a network and the storage attached to it, a NAS is storage that is accessed over a TCP/IP network.

Originating with NFS or CIFS running on a server, NAS has grown to dedicated, specialized devices with high-end features like snapshots, volume copy and replication. Today’s NAS devices support Ethernet connections up to GigE (10-GigE has not yet been widely adopted). However they don’t perform (bandwidth and latency) as well as internal, direct-attached or SAN-attached storage.

NAS is good for environments that need to share data between users or servers and have applications that perform adequately with Ethernet-level performance and file-level access.

SAN storage technology is now very mature. The initial 100MB/sec-transfer rate (1Gb FC) quickly doubled to 200MB/sec (2Gb FC) and now 400MB/sec (4Gb) is readily available. On top of the performance improvements, robust software solutions are available (e.g., shared file systems, snapshots, volume copy, replication, etc.)

NAS solutions have also matured from their humble beginnings. Database vendors now support implementations that use NAS, TOE cards are readily available, enterprise class software solutions are available, etc.

The verdict? The “SAN vs. NAS” war is over. It’s no longer one or the other. Most environments will have a combined SAN and NAS solution. in fact, many NAS solutions actually front-end a SAN to provide an integrated SAN and NAS solution which is the best way to go.

Jim McKinstry is senior systems engineer with the Engenio Storage Group of LSI Logic, an OEM of storage solutions for IBM, TeraData, Sun/StorageTek, SGI and others.